1. Field of the Invention
The present invention relates to a data storage apparatus including both a volatile memory, in which stored data is lost when the power supply voltage is lowered or cut off, and a nonvolatile memory in which storage data is preserved when the power supply voltage is lowered or cut off.
2. Description of the Related Art
In an electronic device designed to store input data, a volatile memory such as a RAM is used as a memory for storing the data. In a volatile memory, stored data is lost when the power supply voltage is lowered or cut off. For this reason, in some devices, a nonvolatile memory such as an EEPROM is used in place of a RAM.
A nonvolatile memory such as an EEPROM, however, has various drawbacks, e.g., a small memory capacity, a limited data write count, and a high voltage for a data write operation leading to large current consumption. Under the circumstances, it is difficult to replace RAMs with EEPROMs at once.
More specifically, in an apparatus in which data are frequently written in a memory, if an EEPROM is used as the memory, and the data write count limit is exceeded, the apparatus itself cannot be used unless the EEPROM is replaced with a new one. In addition, if a battery or the like is used as a power supply, since a data write operation must be performed with a high voltage, the service life of the battery is shortened.